/Engine/Source/Editor/PropertyEditor/Public/MaterialList.h
Add Extra widgets for bottom material value field.
typedef TMulticastDelegate_FourParams< void, const [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [FMaterialItemView](API\Editor\PropertyEditor\FMaterialItemView) > &, [UActorComponent](API\Runtime\Engine\Components\UActorComponent) *, [IDetailLayoutBuilder](API\Editor\PropertyEditor\IDetailLayoutBuilder) &, [TArray](API\Runtime\Core\Containers\TArray)< [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > > & > FOnAddMaterialItemViewExtraBottomWidget